1. Field of the Invention
This invention relates generally to devices for directing the flow of a highly abrasive, atomized slurry from the ejection orifice of an atomizer housing.
2. Summary of the Prior Art
Nozzles for directing the flow of a highly abrasive, atomized slurry from the ejection orifice of an atomizer are well known in the art. These nozzles are typically made of a wear-resistant sintered material such as tungsten carbide, silicone carbide, aluminum oxide, and tetraboric carbide. Although these materials tolerate purely compressive stress, they perform poorly when exposed to tensile or bending stresses. Therefore, various geometries have been employed in an attempt to minimize nozzle cracking caused by the tensile stresses generated by the high centrifugal forces present during atomizer operation.
Three zones of nozzle wear due to atomizer operation are typically observed. First, wear occurs at the inlet of the nozzle due to the circumferential impact of the relatively low velocity slurry media with the high angular velocity nozzle. Second, guide tube wear occurs due to the parallel or laminar flow of the slurry media along the inside surface of the nozzle. Finally, exit wear occurs due to the turbulent flow conditions of the slurry media at the point of flow exit from the nozzle. Exit wear creates performance problems due to the fact that geometrical changes in the flow exit of the nozzle tend to affect the atomizer spray efficiency.
U.S. Pat. No. 3,454,226, Jul. 8, 1969, to Nielsen discloses an atomizer wheel with tapered, semi-cylindrical bushings made from a wear-resistant sintered material configured for mounting within the ejection orifices of the atomizer wheel. These bushings are secured within the ejection orifice solely by the radially outward directed centrifugal forces caused by the operation of the atomizer. The '226 patent teaches that the use of a purely cylindrical bushing results in excessive wear of the inner surface of the ejection orifice where the orifice contacts the outer surface of the bushing. The '226 patent also discloses tapered bushings of a sintered wear-resistant material having a square cross section.
U.S. Pat. No. 3,640,467, Feb. 8, 1972, to Moller, et al. discloses a tapered, semi-cylindrical liner bushing made from a wear-resistant sintered material fitting into a cylindrical sleeve bushing which is configured to mount in the ejection orifice of an atomizer. The '467 patent also discloses a cylindrical sleeve bushing capable of supporting a liner bushing with the shape of an elliptical generatrix. The '467 patent also teaches a prestressing of the cylindrical sleeve bushing through a cooling process to induce a residual, compressive hoop stress on the elliptical generatrix liner bushing. This prestressing allows the liner bushing to better withstand the tensile hoop stress produced by the centrifugal force created by the atomizer operation.
U.S. Pat. No. 3,887,133, Jun. 3, 1975, to Straarup, et al. and U.S. Pat. No. 4,121,770, Oct. 24, 1978, to Straarup, et al. both disclosed a tapered, semi-cylindrical liner bushing supported by a cylindrical sleeve bushing in the ejection orifice of an atomizer. The bushings of the '133 and '770 patents are substantially identical to the bushings disclosed in the '467 patent.
Even though the prior art has proposed various geometrical, material, and manufacturing solutions to the problem of atomizer nozzle wear caused by abrasive slurry media, atomizer spray efficiency and atomizer nozzle wear life remain adversely affected by this problem.